Method of etching metal.



No. 777,278. PATENTED DEC. 13, 1904. J. B. DAVIDSON.

METHOD OF ETCHING METAL.

APPLICATION FILED SEPT. 17, 1903. N0 MODEL.

44 I K /4 0 7/ J f A UNITED STATES Patented December 13, 1904.

PATENT OFFICE.

JOHN B. DAVIDSON, OF DERBY, CONNECTICUT, ASSIGNOR OF ONE-HALF TO CHARLESMUELLER, OF NEW BRITAIN, CONNECTICUT.

METHOD OF ETCHING METAL.

SPECIFICATION forming part of Letters Patent No. 777,278, dated December13, 1904.

Application filed September 17, 1908. Serial No. 173,592. (Nospecimens.)

T0 a/ZZ whom it may concern.-

Be it known that I, J oI-rN B. DAVIDSON, of Derby, in the county of NewHaven and State of Connecticut, have invented anew and usefulImprovement in Methods of Etching Metal; and I do hereby declare thefollowing, when taken in connection with the accompanying drawings andthe figures of reference marked thereon, to be a full, clear, and exactdescription of the same, and which said drawings constitute part of thisspecification, and represent, in

Figure 1, an edge view of a piece of metal represented as coated withvarnish; Fig. 2, a similar view representing a design in dry alkalistamped upon the varnish; Fig. 3, a sectional view representing thealkali in solution and as having eaten through the varnish; Fig. a, asimilar view with the alkali removed; Fig. 5, a similar viewrepresenting the metal as eaten away, the ware exposed through thevarnish.

This invention relates to an improvement in etching metal, andparticularly to theinethod now commonly in use and well known as therubber-stamp method-that is, a method which consists in coating thesurface of the metal to be etched with varnish, then placing upon thevarnish by means of a rubber stamp a solution of potash or other alkali,which removes the varnish, exposing the metal, and then subjecting themetal thus exposed to the action of acid, which eats the metal whereexposed through the varnish. In the method as practiced in order to eatthrough the varnish the alkali solution must be wet, and consequentlycomparatively weak, and in order that the potash shall properly act thevarnish coating must be comparatively thin. With a thin varnish thepotash spreads beyond the impressed design, allowing the acid whenapplied to act upon the metal beyond the desired outline; and,furthermore, with a light varnish, unless the articles are verycarefully handled, the varnish will be accidentally scratched, allowingthe acid to reach the surface of the metal where not desired.

The object of this invention is to permit the use of a heavy varnish,which is less liable to become scratched or eaten beyond the outline ofthe design; and the invention consists in applying the potash in acomparatively dry state, then subjecting the article thus stamped to theaction of vapor, which vapor is taken up by the potash, forming asolution which removes the varnish beneath the potash, as will be morefully hereinafter described, and particularly recited in the claim.

This invention is employed in applying names, trade-marks, or ornamentaldesigns upon the surface of steel and other metal articles which can bedissolved or eaten with acid.

In carrying out my invention the surface 2 of the metal to be etched isgiven a coat 3 of any suitable varnish. Potash or other suitable alkali4: is then applied to the surface or the varnish by means of a rubberstamp having the desired lettering, trade-mark, or ornamental design,and the potash may be comparatively dry, suflic'ient moisture only beingrequired to cause it to adhere to the stamp and being substantially drywill stand up on the varnish, as shown in Fig. 2. The article thusstamped with potash is then subjected to the action of aqueous vapor,and this may be done by placing the articles into a suitable receptacleand then filling that receptacle with aqueous vapor or in any otherdesired manner. The vapor acts upon the potash, which takes up asnflicient quantity to form a solution, and this alkali solution eatsthrough the varnish beneath it, forming an opening 5, as indicated inFig. 3, and exposes the metal corresponding to the applied lettering ordesign. After the removal of the varnish in the de sired design. thepotash is removed by washing, and the article is then subjected to anacid-bath, which acts upon the surface of the metal exposed through thevarnish, the acid eating into the metal, as indicated at 6 in Fig. 5,the surface of the metal acted upon by the acid being the only surfaceexposed through the varnish. l/Vhen the metal is eaten to the desiredextent, the action of the acid is arrested and the varnish removed fromthe article, leaving the desired design etched into the surface.

By using a comparatively dry alkali substance in impressing thelettering or design and submitting the alkali to the action of vapor aheavier varnish may be employed than is possible when a weaker alkalisolution is used as in the methods now used, and it is less liable to bescratched or unintentionally removed around the edges of the design, andby employing drier or stronger alkali solution the varnish is moreperfectly removed and the outlines of the design are sharper or moreclearly defined and allows a deeper etching of the metal with lesspossibility of the acid acting through the varnish outside of thedesign, producing an acid-bitten cloud on the metal.

Having fully described my invention, what I claim as new, and desire tosecure by Letters Patent, is

The herein-described method of etching metal consisting in coating thesurface to be etched with a varnish, placing upon the varnished surfacelettering or a design in a comparatively dry alkali solution, thensubjecting the article to the action of aqueous vapor whereby thevarnished surface beneath the alkali will be removed, then subjectingthe surface thus exposed to the action of acid, whereby the metalexposed through the varnish may be eaten, substantially as described.

In testimony whereof I have signed this specification in the presence oftwo subscribing witnesses.

JOHN B. DAVIDSON.

Witnesses:

WILLIAM S. MORGAN, I GEO. (J. ALLIs.

